Speedo Reading

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Running on 35s is defo a under read. Speedo says 50 , I'm actually doing 56 ish
So I (nearly) always have my sat nav on with the speed alarm on:D
 
This is strange, theory says you should be greatly over reading. Must be different per vehicle :nenau
 
what are 31s, are they new tyres for the wheel or a complete set of new wheels assembly as i have exactly the same problem as the op

Most tyres these days are in metric measurements like 235/70R16 but you can also get tyres in the old imperial sizes aswell like 31/10.5R15 but in the 4x4 world most people convert their metric sized tyres to imperial measurements & if you've standard size tyres on yours they work out at about 29" hope this make sence to you TBH it doesn't bother me that my speedo is over reading as it just means i'm less likely to get done for speeding
 
Most tyres these days are in metric measurements like 235/70R16 but you can also get tyres in the old imperial sizes aswell like 31/10.5R15 but in the 4x4 world most people convert their metric sized tyres to imperial measurements & if you've standard size tyres on yours they work out at about 29" hope this make sence to you TBH it doesn't bother me that my speedo is over reading as it just means i'm less likely to get done for speeding

if i were to upgrade my standard tyres to 31" would they fit on the same wheels or would I need a new set, also will they fit to a unmodded car?
 
if i were to upgrade my standard tyres to 31" would they fit on the same wheels or would I need a new set, also will they fit to a unmodded car?


think ive cracked it, just need to upgrade to 235/80R16 in metric and that should work out about right, correct me if I'm wrong
 
Yes you can fit 31" tyres onto standard rims:thumb2 now some T2's 31's fit on without any probs yet others the tyres can catch/rub on the front bumper & the front mud flaps, most just remove or trim back the mud flaps (mine are now shorter & narrower:augie) & with the front bumper I think it's the bottom edge that can catch which people trim back. Finding 235/80R16's might be hard to find but 255/75R16's are very common & around the same price as the standard size T2 tyres as I fitted a set to my disco a couple of years ago but can't remember what they work out at 30-30.5" I think:confused: but will check
 
Have finaly confirmed that speedo error (20%+ @ 30 mph falling to 10%+ as speed rises over 60 mph) also applies to odometer. Same run 0f 141 mles (according to satnav) reads 143 at average 55mph but 148 at average 50mph. Readings have been consistant over 4 runs.
This is mostly m/w towing 1.6T caravan. So not too bad realy, but I suspect it is much worse (overreading at least 10/15%+) as the speed drops towards 30mph, there is no way I'm doing 141 miles that slowly to find out LOL! Yes I do know that there are distance post on m/w's but it's dangerous enough already, judging by some of the idiots I encountered on M5, M42, M6 etc., without me crawling along & making it worse.

Noticable that at 55/60 the truck seems more eager than at 50/55, & stays in o/d longer. Fuel consumption appears better also, but there are too many variables to be sure.
So in future I'm not driving so slowly so as to get there faster, in less miles & using less fuel LOL.
 
I have to agree on this, every car I have had read about 5% low as standard, I did wonder if the different tyre pressure could make that much difference by changing the rolling circumference :nenau.

On the current Patrol with 285/75/16 tyres, it is almost spot on.:thumbs

Ian
 
i have 2 t2 on the road and 1 is reading faster than nav but the other is as good as spot on to nav.both with 235/75/15 on them.
i have to make a mental note of the speed for the car i am using.
 
Both my old T2 and my latest one are well out compared to a sat nav, Our Fiesta MK6 is spot on, The MAN truck at work is spot on too.
 

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