mgbphilippe123 a écrit :Moi, je remets une pierre à l'édifice:
Determining the best tire size to buy for your MGB is a popular discussion among owners. Leaving aside the question of brand preference, it of course depends a great deal on what size rims you have, wire or steel, and whether they are original equipment or not. I'll try to cover some of these issues in this article, and hopefully answer your questions.
Replacements for Stock Tires
The first and most common question is what is the modern equivalent for the OE (Original Equipment) tire size, specified as 155R14 or the old replacement 165R14. This translates as a tread 165mm wide, which fits on a 14in rim. You can find tires in the size specified as this, but they are often expensive "period reproduction" tires from specialist suppliers. For quite a few years, tire sizes have been expressed in a standard way with an extra set of numbers to the above, namely, the sidewall ratio.
Why do you want to maintain the stock tire diameter? Well, the main reason is that if you change the tire diameter, your speedometer will read either faster than actual speed (shorter tires) or slower than actual speed (taller tires). This may be desirable; shorter tires will increase your 0-60 times, but reduce your top speed, and taller tires will do the opposite.
I've seen articles that state that the BGT used 165 and the B used 155 tires, but I don't see any proof of this, as the part number charts I have show the same speedometer fitted to the B and BGT. If they had different sized tires, they would require different speedometer gearing ratios.
Thanks to some clever math (not by me), the "implied" sidewall ratio for the orignal tires was calculated to be 78 (height = .78 * width). Anyone that has been tire shopping in the last 10 years will know that finding tires with sidewall ratios greater than 70 is tough, especially with the trend towards lower profile tires on ever-larger rims. The first task then, is to find the original diameter of the original tires, so that we can calculate some possible modern replacements. Assuming the original sidewall ratio of 78 (if this is inaccurate, someone please tell me!) we get the following:
Size Diameter (mm)
155HR14 597.4
165HR14 613.0
So, calculating diameters for some common metric tire sizes, we get:
Size Diameter (mm)
175/70R14 600.6
175/65R14 583.1
185/70R14 614.6
185/65R14 596.1
185/60R14 577.6
195/60R14 589.6
Now we can introduce another constraint - the width of the rim you're mounting the tire onto. The rim is not supposed to be less than 7/10ths as wide as the tire's section width. For the stock 4.5" rims, this works out to 163mm, rounded to 165 - but we're not going to find any sidewall ratios of 80. 175 tires are supposed to go on 5" rims, but some manufacturers say 4.5" rims are OK. 185 tires are certainly pushing the limit, as they are designed for a 5.5" rim, and you risk sidewall roll or debeading on extreme cornering, which could be very dangerous if you're trying to execute and emergency manoeuver.
So, since the 175/65R14 is way too short, we're left with the 175/70R14 as the best stock replacement. This size is fitted to some Saturns, but your brand selection in this size may be limited. The good news is they will probably be cheap, as tire companies make their margins on the "bling bling" low profile tire craze.
Source:
http://www.mgexperience.net/article/tire-sizes.html
A+
Philippe.
Un pneu 175/70/14 doit avoir un diamètre de l'ordre de 600 mm et c'est très insuffisant. Il n'est pas étonnant qu'avec cette monte trop basse la voiture touche sur les ralentisseurs ! Si on veut supprimer ce désagrément, il faut des pneus qui conviennent à la voiture, de préfèrence du 165X14, et si on veut encore plus de sécurité sur ce plan il y a la solution d'un échappement avec un intermédiaire du type "bomb-box"...grâce à cela, je ne toucherais plus les casse-vitesses...???
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