Bicycl Road Tire Rolling Resistance Tests

Road Tire Rolling Resistance Test Discussion

Below are some comments on rolling resistance testing from Jobst Brandt, who provided the test data. These are postings to the newsgroup rec.bicycles.tech, and they have been left unedited.

Rolling Resistance Main Page Terry's Bike Information Page

From: Jobst Brandt (jbrandt@hpl.hp.com) Subject: Re: Skinny tires more resistance Newsgroups: rec.bicycles.tech Date: 1999/01/28 Simon Kellett writes: > My impression is that no-one has been able to do reliable tested > that remove unwanted variables, notable differing tyre constructions > and pressures. You need a tyre available in many widths but with > identical construction and tread and designed running pressures. The only variable that throws this sort of testing off is the inflation pressure and because it has a large effect on RR the comparison is difficult to assess. With various tire cross sections, different pressures must be used. The question is how much and to what do you tie the inflation. One way would be to inflate tires according to a sliding scale based on cross section because casing stress is directly proportional to tire cross sectional diameter. Therefore, tires could be inflated to the same casing tension as a normalizing parameter. However, complaints would most likely be heard immediately from manufacturers whose tires fared less well, claiming that the tire was under inflated. Rolling resistance tests are relatively simple, once a rolling test stand is built. In such a test, the drum on which the loaded wheel rolls is brought to a desired speed and allowed to coast down to a lower speed while counting the number of revolutions and fractional revolutions. This is a standard coast-down test that has been widely used. Although the results are peculiar to each machine they can be converted to drag force making a one-time drag measurement to determined a conversion factor for distance to drag force. Jobst Brandt <jbrandt@hpl.hp.com>

From: Jobst Brandt (jbrandt@hpl.hp.com) Subject: Re: tubular tires Newsgroups: rec.bicycles.tech Date: 1998/03/19 Mike Sullivan writes: >> I have posted the rolling resistance tests done by IRC > I'm sorry but I am not familiar with these tests, is it possible to > repost them? Where were they performed? Whose facilities were used? > What tires were they tested against. And when were they performed? > Curiosity. You can have the data, but I should explain what it shows. This information is contained on the data sheet but may not be obvious. The tires were mounted on the same rim with the tube offered for that tire by the manufacturer. Tubulars (2) were glued onto the rim with standard practice using tubular glue. All tires were run against a smooth steel drum with the same load at a range of inflation pressures. What is shown by fitting a power curve to the points is that the data is consistent with little scatter, and that all tires fit into a family of rolling resistance curves that do not cross and are essentially the same equation. The exception was the tubular tires that were offset by a constant from their proper curve so that they crossed other tires. This constant offset was causes by rim glue losses that depend on load alone and are not affected by inflation pressure. Therefore, tires with low rolling resistance don't get much better the harder they are inflated and have a flatter characteristic over the range of inflation pressures while high rolling resistance tires have a steeper slope, getting better the less they flex but never as good as a low RR tire except toward infinite pressure where none would have any flex or RR. Of course these tires all had smooth or nearly smooth tread patterns. >> Both tubulars and clinchers are completely round in cross section in >> the portion free of the rim. There is no way of causing any other >> shape with a uniform bias ply casing. > I'm not sure if I understand this, if a portion of the clincher is > mounted inside the rim, and a portion of a tubular is mounted on the > rim, then where is the cross section measured and I assume when you > say round you mean "literally" round as in an equal distance as > measured at all points of the inside and outside of the tire when > inflated and with no weight applied. The casing is a thin walled fabric that supports the tensile stress of containing the inflation pressure. THis casing is circular in cross section wherever it is not in contact with the rim for both tubulars and clinchers. Where the tire is in contact with the rim, it has no effect on tire compliance of supporting a wheel load. Therefore, that open face of the clincher as the underbelly of the tubular have no effect on tire deflection. >> Avocet TT, which is based on the Criterium > Are these tires made by CST or National? This is not a knock, just > couldn't find one to check myself. Avocet tires are made by IRC. >> Therefore, tires like the Avocet TT, which is based on the Criterium >> but with a thinner tread, has the lowest RR and is the most tubular >> like of these tires. If it were fitted with a thin walled tube it >> would not only be better than a glued on tubular that it already is, >> but it would beat a tubular with hard glue. Rolling resistance is casued by rubber deformation losses in the tread, the tube and the casing. The tube is firmly attached to the casing by inflation pressure so it is like a tread inside the tire. The whole tire flexes in three dimensional space, X, Y and Z. You can verify this typically by laying a stadard business card between tire and tube. It will shred to fine confetti when ridden. It is this motion that causes hysteretic loss in the elastomer in the casing, the tread and the tube. If the tire has patterned tread, such as a knobby tire has in the extreme, deformation of the tread into the voids will cause additional loss. That is why knobby tires roill so poorly. Unfortunately, I cannot locate the tire test with that included the Vittoria CX and Clement Criterium tires. These must be in the Avocet archives. As you see these tests were done 12 years ago and the following is only one of the series of tests that were performed. Others tested the effect of various tubes in the same tires. I only have this sample now the rest must be on some backup tapes floating around here. Jobst Brandt <jbrandt@hpl.hp.com> ------------------------------------------------------------------------ Tires, AVOCET and SPECIALIZED, 18 Apr 86 Rolling resistance (g) vs. inflation pressure (kg/cm2) @ 50 kg load Tire ID Size Sample Nominal wt Measured wt Width +-0.2 TPI ------- ---- ------ ---------- ----------- ----------- --- Col 1 - Air Pressure (kg/cm2) Col 2 - S Turbo/LR 700x25C (A) 205 234 21.4 116 Col 3 - S Turbo/LR 700x25C (B) Col 4 - S Turbo/LS 700x25C (A) 205 243 21.4 106 Col 5 - S Turbo/LS 700x25C (B) Col 6 - A Criterium/20 700x25C (A) 225 236 23.1 66 Col 7 - A Criterium/20 700x25C (B) Col 8 - A Timetrial/20 700x20C (A) 215 214 21.0 116 Col 9 - A Timetrial/20 700x20C (B) Col 10 - S Turbo/LR 700x28C (A) 225 291 24.9 66 Col 11 - S Turbo/LR 700x28C (B) Col 12 - S Turbo/LS 700X28C (A) 225 299 24.9 66 Col 13 - S Turbo/LS 700X28C (B) Col 14 - A Road/20 700x28C (A) 265 272 25.2 66 Col 15 - A Road/20 700x28C (B) Col 16 - S Turbo/R 700x25C (A) 180 188 21.0 116 Col 17 - S Turbo/R 700x25C (B) Col 18 - S Turbo/S 700x25C (A) 180 193 21.0 116 Col 19 - S Turbo/S 700x25C (B) Col 20 - A Criterium/30 700x25C (A) 190 182 22.6 66 Col 21 - A Criterium/30 700x25C (B) Col 22 - A Timetrial/30 700x20C (A) 165 168 20.2 106 Col 23 - A Timetrial/30 700x20C (B) Col 24 - S Turbo/R 700x28C (A) 220 248 24.8 66 Col 25 - S Turbo/R 700x28C (B) Col 26 - S Turbo/S 700x28C (A) 220 253 24.8 66 Col 27 - S Turbo/S 700x28C (B) Col 28 - A Road/30 700x28C (A) 230 241 25.0 66 Col 29 - A Road/30 700x28C (B) c1 c2 c3 c4 c5 c6 c7 c8 c9 c10 c11 c12 c13 c14 c15 c16 c17 c18 c19 c20 c21 c22 c23 c24 c25 c26 c27 c28 c29 3.5 356 365 395 369 367 392 348 347 430 443 423 432 423 406 355 364 382 386 378 387 361 369 419 432 427 442 394 403 4.0 322 329 360 343 337 361 319 316 393 401 391 393 386 376 325 333 352 356 350 357 325 331 390 390 395 401 360 363 4.5 298 302 330 319 316 336 296 290 366 373 362 368 354 347 297 309 326 332 322 329 301 302 364 362 369 375 334 331 5.0 279 282 311 298 294 314 280 271 341 348 335 345 335 320 275 289 311 311 302 307 282 284 340 339 342 351 311 310 5.5 265 268 293 287 279 297 265 255 324 329 319 327 319 305 262 276 295 296 284 295 268 267 320 322 325 333 290 289 6.0 255 253 282 274 267 282 249 242 310 312 306 310 303 293 248 260 283 285 269 281 253 252 305 304 311 318 275 273 6.5 244 242 274 264 254 269 239 230 297 294 292 297 290 283 237 253 275 277 257 270 244 242 292 291 298 309 266 262 7.0 238 232 263 255 247 256 229 221 287 284 282 288 280 273 231 245 267 270 247 261 235 232 281 283 286 299 254 249 7.5 231 226 255 250 238 247 222 213 272 277 272 279 272 264 222 236 260 260 238 249 228 224 272 272 274 289 248 242 8.0 222 219 248 244 233 239 215 205 265 267 266 272 264 258 216 230 253 253 231 241 223 217 263 264 273 281 243 235 8.5 216 212 244 237 226 231 209 201 259 259 259 266 257 252 208 223 245 246 223 233 216 209 256 257 0 274 235 229 9.0 213 211 241 236 223 224 204 195 255 256 259 259 254 245 204 219 245 245 222 231 212 208 252 256 0 273 233 226

From: Jobst Brandt (jbrandt@hpl.hp.com) Search Result 4 Subject: Re: tubular tires Newsgroups: rec.bicycles.tech Date: 1998/03/20 View complete thread (160 articles) This data set includes the tubulars and Michelin tires. ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ You can have the data, but I should explain what it shows. This information is contained on the data sheet but may not be obvious. The tires were mounted on the same rim with the tube offered for that tire by the manufacturer. Tubulars (2) were glued onto the rim with standard practice using tubular glue. All tires were run against a smooth steel drum with the same load at a range of inflation pressures. What is shown by fitting a power curve to the points is that the data is consistent with little scatter, and that all tires fit into a family of rolling resistance curves that do not cross and are essentially the same equation. The exception was the tubular tires that were offset by a constant from their proper curve so that they crossed other tires. This constant offset was causes by rim glue losses that depend on load alone and are not affected by inflation pressure. Therefore, tires with low rolling resistance don't get much better the harder they are inflated and have a flatter characteristic over the range of inflation pressures while high rolling resistance tires have a steeper slope, getting better the less they flex but never as good as a low RR tire except toward infinite pressure where none would have any flex or RR. Of course these tires all had smooth or nearly smooth tread patterns. >> Both tubulars and clinchers are completely round in cross section in >> the portion free of the rim. There is no way of causing any other >> shape with a uniform bias ply casing. > I'm not sure if I understand this, if a portion of the clincher is > mounted inside the rim, and a portion of a tubular is mounted on the > rim, then where is the cross section measured and I assume when you > say round you mean "literally" round as in an equal distance as > measured at all points of the inside and outside of the tire when > inflated and with no weight applied. The casing is a thin walled fabric that supports the tensile stress of containing the inflation pressure. THis casing is circular in cross section wherever it is not in contact with the rim for both tubulars and clinchers. Where the tire is in contact with the rim, it has no effect on tire compliance of supporting a wheel load. Therefore, that open face of the clincher as the underbelly of the tubular have no effect on tire deflection. >> Avocet TT, which is based on the Criterium > Are these tires made by CST or National? This is not a knock, just > couldn't find one to check myself. Avocet tires are made by IRC. >> Therefore, tires like the Avocet TT, which is based on the Criterium >> but with a thinner tread, has the lowest RR and is the most tubular >> like of these tires. If it were fitted with a thin walled tube it >> would not only be better than a glued on tubular that it already is, >> but it would beat a tubular with hard glue. Rolling resistance is casued by rubber deformation losses in the tread, the tube and the casing. The tube is firmly attached to the casing by inflation pressure so it is like a tread inside the tire. The whole tire flexes in three dimensional space, X, Y and Z. You can verify this typically by laying a stadard business card between tire and tube. It will shred to fine confetti when ridden. It is this motion that causes hysteretic loss in the elastomer in the casing, the tread and the tube. If the tire has patterned tread, such as a knobby tire has in the extreme, deformation of the tread into the voids will cause additional loss. That is why knobby tires roill so poorly. Jobst Brandt <jbrandt@hpl.hp.com> ------------------------------------------------------------------------ 700x25C, 700x28C Tires and Vittoria and Clement Tubulars Rolling resistance (g) vs. pressure (kg/cm2) @ 50 kg load Col 1 - Inflation pressure (kg/cm2) Col 2 - S Touring 25C Col 3 - S Touring II 25C Col 4 - S Ultra L 25C Col 5 - S Turbo 25 Col 6 - M HiLite Comp 20C Col 7 - Avocet 20 25C Col 8 - Avocet 30 25C Col 9 - Vittoria CX Col 10 - Clement Seta 250 Col 11 - S Touring 28C Col 12 - S Touring II 28C Col 13 - S turbo 28C Col 14 - M HiLite 23C Col 15 - Avocet 20 28C Col 16 - Avocet 30 28C c1 c2 c3 c4 c5 c6 c7 c8 c9 c10 c11 c12 c13 c14 c15 c16 3.5 576 531 480 444 493 421 417 423 408 531 521 508 434 390 384 4.0 522 483 437 408 440 390 377 398 385 484 472 453 389 360 356 4.5 483 441 399 378 399 365 343 380 366 451 433 415 358 340 331 5.0 452 408 373 353 374 345 326 362 351 423 403 388 339 322 311 5.5 427 379 351 334 350 327 309 348 339 403 381 369 320 307 296 6.0 402 359 334 316 330 312 293 336 330 384 362 351 302 295 283 6.5 379 340 320 301 311 299 281 327 321 370 347 334 287 284 270 7.0 362 324 309 287 296 285 270 321 314 357 333 322 277 274 260 7.5 348 313 297 277 281 274 260 317 307 344 321 311 267 267 250 8.0 335 301 286 267 270 267 254 311 302 335 312 302 260 259 243 8.5 323 294 280 261 259 260 248 306 294 329 305 295 254 252 238 9.0 312 285 273 255 256 256 242 305 289 323 300 290 249 248 234

Newsgroups: rec.bicycles.tech Subject: Re: Tire Resistance Ratings Date: 3 May 2001 17:58:09 GMT Stephe Thayer writes: > I'm I the only one that finds it odd that the Avocets have ALL the > lowest rolling resistance on this chart and that also just happens > to be the company Jobst works/worked for? The tests were performed in Japan by the rubber institute and Avocets are not the only low RR tires. As I pointed out, if the tubulars had been mounted with hard glue, they would have been even lower, as one would expect from the thickness of the tube, casing and most importantly, tread. After all, flexing of elastomers is where RR occurs and at the time of these tests, Avocet was the first to use a new thinner but more durable tread rubber made by IRC. It was the introduction of this rubber to bicycle tires that increased tread life greatly while also improving traction. That was the incentive to make the picture of high speed cornering to show that this tread has good traction and that slicks corner well. http://www-math.science.unitn.it/Bike/Countries/Europe/Tour_Reports/Tour_of_the_Alps_Gallery/ The age of these tests and the picture is apparent from the old toe clips and straps. The pilot run of these tires suffered from Firestone delamination (and probably for the same reason) because the new compound did not adhere well to casings. The solution IRC found was to make the tread of two layers, the first, a thin layer of the old tread rubber that is inferior but adheres well to casings, and the second the wear layer that adheres well to the old rubber. Firestone/Bridgestone seems to have not chosen this costly step without success. The two layers turn out to have another benefit in that it gives a warning that there is about 100 miles of tread left when the color changes. Both rubbers are black but distinguishably different in surface texture. What should be noted is that no one has made subsequent RR tests that are anywhere as comprehensive and inclusive of tires on the market. I suspect there is little interest in the subject from what I see on the road. Fashion is far more important to the current market, so why belabor the subject of functional differences between tires. That's not where it's at. No one gives a hoot that colored tires have poor traction, especially in the wet, and that they wear out fast, but they cost more to make up for that. Jobst Brandt <jbrandt@hpl.hp.com>