What are the implications, Construction and Use Regulations, and changes to the behaviour of the Car on the Road, if 155/70 R14 tyres are fitted in lieu of 165/65R14?
That is definitely a good question. The handling of the vehicle might change a bit in cornering situations or snow/ice conditions with a thinner tire than what we already have. It should help with LRR and as long as the speed and load ratings aren't exceeded, under most conditions there might not be any issues. The contact patch at the same pressure should be longer in terms of weight distribution but tire structure might change how the patch is formed too. I think our rims can fit a narrower tire to a certain margin. I'm not sure of the rules in the UK but in the US, our tire shops usually refuse to do any alignment or size outside of stock sizes but usually with a little searching we can find a shop that could do it.
This might be a decent direction to go now that the Bridgestone B391 sounds to be going out of supply in the UK. Will it do better than the stock tire? I'm not sure.
My last car was a smart 42, and the standard tyre sizes were 145 front & 155
rear, and with that combination the small & short car is very sensitive to
crosswind, almost impossible to hold a straight line.
A common mod. on smart's are to fit 155 front & 165 or 175 rear, that makes it a total different car.
Going from 165 to 155 on an Insight may have the reverse effect, and make the car sensitive to crosswinds.
Also not sure how wide a rim is recommended for a 155 tyre. ?
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John, proud owner of the only I1 in Denmark.
The specifications for the tyre call out what range of wheel width is acceptable. For example, the OE Potenza tire can be fitted to 4.5"-6.0" wheels, and the Insight's wheels are 5.5" (140mm, versus the 165mm nominal tread width).
There's a page on the Barry's Tire Tech site that says that wider tyres actually have lower rolling resistance, all else equal. But in practice, tyres have such terrible aerodynamic drag that narrower is better. The Insight's 165mm width seems like a happy middle ground.
Handling implications? I won't hazard a guess.
Get the full spec sheet for the tyre, including load carrying capacity.
What are the implications, Construction and Use Regulations, and changes to the behaviour of the Car on the Road, if 155/70 R14 tyres are fitted in lieu of 165/65R14?
The two sizes share rolling diameter to within 0.4% so no changes to speedometer reading.
The reason I pose this question, I notice that on the AdAC website, there could be a significant benefit in LRR for the narrower tyre.
I can offer my experience with a 155/80/13 tire vs. the 165/65/14 Potenza.
I believe a narrower version of the same tire brand and model would yield LOWER rolling resistance all else being equal. My 155/80/13 tires for winter do hurt MPG likely due to tread pattern, tire weight (the 155's are heavier by several lbs. per tire than the 165 stock Bridgestone Potenza tires). Of course, the 155's are a different tire manufacturer AND a different model of tire than the stock 165. So, I'd bet the 155/70/14's might net you a slight increase in MPG's (i.e. lower RR) if they are the same manufacturer and model. I'd be interested to see results of a controlled test of this theory.
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2003 Silver 5 speed - MIMA & Grid Charger on the way
RR primarily comes from the belt stiffness in the tyre and how willing it is to deform on as it rolls along the tarmac, this is tweaked by tyre pressures but the insight tyres is 40% lower RR than a similar RE92 of another size. I really don't think anything will beat the insight tyre, its RRC is so low.
I had a look around the internet to try and find out whether switching to a smaller tyre would be illegal. I couldn't find anything - the closest relevant part is that tyres used must have a suitable load and speed rating - which the 155/70/14 tyre examples I looked at do. The best UK tyre law summary I found is here:
An interesting point is that all tyres must have an 'E marking' or they would be illegal and that may limit us importing RE92's from the USA. I also looked for 155/70/14 tyres and only found two examples a Hankook and a Continental Premium Contact which is likely to be sticky / have poor LRR.
If we could get Michelin Energy Saver in 155 size, it might be worthwhile?
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2005 Insight, UK Spec Silver 5 speed with Alpine stereo, subwoofer & speakers with iPod link, IMA C&C, Shark Fin Aerial, Garmin EcoRoute HD, Skinz sound deadened rear shelf, 'InsightCentral' number plates, 19" rear wiper, Osram nightbreaker plus bulbs
Previous owner of 1999 Japanese Silver 5sp, 2001 UK Citrus 5sp & 2000 Japanese Red CVT Honda Insight - An extraordinary car for ordinary people
Going from 165 to 155 on an Insight may have the reverse effect, and make the car sensitive to crosswinds.
My max. speed on the highway is 62 mph and I already can feel how sensitive the Insight is with 165 tires compared to other cars. I would not go smaller.
The results from ADAC organisation indicate that the lowest performing narrow tyres match or beat the best of the slightly wider tyres for LRR.
Hence my what / if thinking, if the car ran on the best LRR 155/70R14 tyre, would we see a performance matching the coveted B391?
Are those the results that have a 0-5 rating rather than emperical data?
The Audi A2 1.2 (3 litre) had the B381 in a size like that, again discontinued and it wasnt quite as low as the Insight RRc as far as I know.
My issue with RE92 now stems from the tread between them and the B391 being TOTALLY different, also I will have to check with the insurance company over non E rated tyres..... we saw what happened in the UK when people were fitting winter tyres and getting charged more.
Ill add to my thread later and post my current findings with the Fulda EcoControl I have.
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Reduction in Tyre Width on an Insight?
