Club 80-90 Forums

Looking for some advise really.

Got a 1.9 bigbore petrol panel van and am running 17" Porsche cup alloys 205/40 on front and 255/40 on rear. Just worked out my fuel consumption and it's 14.7mpg, which I am guessing is a bit steep, my wallet certainly seems to think so!!

Saw some alloys on eBay which are 15" and 195/50. Do you think I will see much of an increase in mpg? Is it worth doing as I do rather like my other alloys!!

Has anyone else up sized/down sized and noticed a difference? Got a baby on the way and seeing if I can squeeze more economy out of the van before even considering selling it!!

Thanks for you help

Gas it. Get it properly tuned.... a std DG should get ~22mpg on fool's gold.

Ian

the overall size of your wheels should not be that much different between 17 inch wheels and 15inch due to lower tyre profile i have a slightly tuned engine probably slightly higher tuned than a 1.9 and i get nearly 30mpg on a run and i am running 18 inch wheels, i would look at servicing your van or make shure the wheels are not binding as my 1.9 camper does around 24mpg on a run also make shure you are running the correct gearbox for your engine easily checked with gearbox code

At a guess its not a true reflection as your speedometer will be very inaccurate with big wheels , unless you are using a GPS

if its reading 25% wrong, you could be getting 19mpg, which is about right round town

With an engine capable of driving them with enough power (so its not being lugged all the time to get up to speed) would be more efficient on longer runs with bigger rolling radius which has effectively upped the gearing. Stop start traffic less so. Increased stress on gearbox and drive shafts may well lead to failure sooner than with standard engine as components being pushed towards limits. Thats my armchair physics take on it.

LPG its the future......or diesel

Fuel savings with bigger tyres will be so marginal as to be a waste of time. Learn to drive differently or change fuel type. My rule is NEVER EVER touch the throttle unless you really have to

Compared to standard 185R14's your wheels are both smaller:
Minus 9.56% on the fronts.
Minus 3.49% on the rears.

As your rears are the driven wheels the engine revs will be just 3.49% higher at any given speed so not massively under geared.
But
The fronts are nearly 10% smaller so as the speedo takes it's drive from the front the speedo is going to read and record 9.49% higher so your 14.7mpg is actually around 16.1mpg

As T25 speedo's already over read 8 - 10%, then adding an additional 9.5%, your speedo is going to read near 18% more than actual GPS 'True' .............something like a display reading of 71 with a true GPS speed of around 60mph.

Martin

Thanks for the reply.

Noticed a slight increase when I did a much needed oil change. Will look at air filter and tune. Gearbox is a five speed (panel van) and the engine is a engine shop reconditioned so you might be onto something, will look into it.

Thanks

Thanks for the responses. Use GPS for the speedo/miles. Noticed a small difference with an oil change and has been mentioned that cleaning air filter would help. Might get it tuned but no idea who I would take it too in Brighton area!!

bigdogbsc wrote:Thanks for the responses. Use GPS for the speedo/miles. Noticed a small difference with an oil change and has been mentioned that cleaning air filter would help. Might get it tuned but no idea who I would take it too in Brighton area!!

Oh! no google in your area?....

come on type engine tuning, Brighton in google and then phone a few of the garages that do it, ask questions tell them what you have etc...

Regal Autosport have rolling road facilities..
if they can't do it ask who can