185/80x15 tyres
hotrodsurplus:
Just to be specific, the common callout for this tire size is the old Euro Metric standard, 185R15. The Euro Metric callout assumes an 82-percent aspect ratio. The Vredestein, Dunlop, Avon, and Pirelli models are such tires: 185HR15 or 185VR15 (the H and V are speed ratings). That's the common radial analog for the 6.40-15 tires on cars like E-type Jags and Austin-Healey 3000s.
That differs from the later standard Metric callout that some brands use, 185/80R15. Based on my research the tires available in that size are for commercial (truck and van) use.
So don't just assume that a 185R15 and a 185/80R15 tire are the same. They're not, if only for aspect ratio. And the two point spread between the two ratios is enough to make a difference. Calculations based on the callout size show the 185/80R15 is 26.7 inches tall where the 185R15 is 27 inches tall.
Yes, both of these tires are taller than the stock 5.60-15. The 5.60-15 ranges from 25.75 to 25.9 inches tall depending on manufacturer and model. Understand that the 165r15 radial analog is shorter, 25.4 to 25.6 depending on manufacturer and model.
I prefer the 185r15 on the back of a Beetle for three reasons.
1) they raise the effective gear ratio. That reduces the engine speed by about 140rpm. For comparison sake, the jump from a 4.37:1 gear to a 4.12:1 gear reduces engine speed by 170rpm. So tThe engine in a car with a 4.37:1/.89 gearbox and 185r15 tires will spin only 30rpm faster than the engine in a car with a 4.12:1/.89:1 gearbox and 165R15 tires.
2) they better fill up the unsightly gap between the tire OD and the wheel arch on a stock-height car.
3) the taller size lets you decamber a swing-axle rear to a degree or so negative camber for stability reasons yet the rear of the car remains effectively stock height. That's very important as a stock swing-axle Beetle has 2.5 degrees positive camber to '66 and a degree positive camber from '67 onward. Positive camber on the back of a swing-axle car promotes wheel tuck which will induce intense oversteer which can cause a spin and possibly a rollover. You can still go quite low with a 185r15 tire--it's only .6 inches taller than a 205/70 and people go quite low with those. But as cal-look snobs we don't slam cars anyway. That's for the idiots who came from the minitruck scene, right?
The caveat, of course, is whether a car can pull the taller tire. I know from experience that a stock 1600 with a 12V trans (4.12:1) will pull a 27-inch-tall tire quite handily. It will reduce engine speed and cabin noise and I never noticed that i had to reach for third gear to climb hills any more than I did with 165s. But a stock 36er or 40-horse engine may not be able to pull a 185r15 tire even with a 4.37:1 transaxle. There was a reason that Volkswagen used the 4.37:1 and 4.44:1 ring/pinion with those engines: they're not very strong.
I did lots of research before I bought my Vredesteins. I have 155r15s for the front and 185r15s for the back based largely upon alstare84 and christoph's cars. I like the wheel/tire fit of both cars although I think they could come down just enough to get negative camber in the rear--less than an inch for sure. Those cars have 5.5 wheels on the back but the 185R15 fits well on a 4.5-inch rim. It's a little bulgy but not offensive. A 5.5 would be better and I'm having a set of P-car wheels widened to those specs for that reason.
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RichardinNZ:
Thanks for the additional information; very useful. What are the p-car rims (I think I've missed something obvious)?
regards
Richard
hotrodsurplus:
Quote from: RichardinNZ on April 09, 2013, 08:02:54 am
Thanks for the additional information; very useful. What are the p-car rims (I think I've missed something obvious)?
You're welcome. P-car is Porsche.
RichardinNZ:
I did wonder whethe that was the case! Thanks
Richard
streetvw:
here's another angle the combination in this shot is front 4.5" with 145 XZX Michelins and rear 5.5" with 185 XWX Michelin's
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