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27" tires. Will it cause overheating issues?!?
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MidWesty79
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PostPosted: Mon Feb 12, 2018 9:12 am    Post subject: 27" tires. Will it cause overheating issues?!? Reply with quote

Hello all, I have looked through the Tire sticky and since the BF Goodrich KOs are no longer available, I am considering the General Grabber AT2 27X8.50R14LT. People seem to be quite happy with them overall.

My concern is possible overheating. I have a '79 Westy that I enjoy taking on long road trips. Last year I covered roughly 5000 miles through the Rockies and across the plains. And this year I hope to have the opportunity to double that.

My concern is what I believe to be a 5.5% decrease in tire RPMs (vs the 195/75/14 tires currently on the bus,) which would lead to a 5.5% decrease in engine RPM with the larger tires. My bus runs hot as it is. It always has. I would like to have the added ground clearance and offroad traction provided by something like the Grabber, but I am somewhat concerned about the power and overheating effects of long days at highway speed.

Anyone have any experience with engine temps effected by these, or other larger diameter tires?
Thanks!!
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Wildthings
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PostPosted: Mon Feb 12, 2018 10:05 am    Post subject: Re: 27" tires. Will it cause overheating issues?!? Reply with quote

I have General Grabbers in my '77, but I had a tranny built to match. So my highway rpm didn't change very much, while my lower gears are still a bit shorter than stock.

I did run an 091 tranny coupled with my 1800 for two decades and 215/70r14 (25.9") tires and it was just fine, so I doubt you will have much of a problem with an 091 tranny, a 2.0L engine, and 27x8.5r14 (26.8") tires.

I am very happy with the Grabbers at this point in time. Wink
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Randy in Maine
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PostPosted: Mon Feb 12, 2018 11:24 am    Post subject: Re: 27" tires. Will it cause overheating issues?!? Reply with quote

Really one for the "tires thread" but stock size is 185R14 or about 25.66" tall or ~786 revs per mile. A 27x8.50x14 is about 27" tall and about 747 revs per mile.

Do you run a good CHT and that allows you to monitor the temps? Might be worth having.
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asiab3
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PostPosted: Mon Feb 12, 2018 11:39 am    Post subject: Re: 27" tires. Will it cause overheating issues?!? Reply with quote

Crossing the Rocky Mountains and you're making your effective gear ratio taller? Shocked

The engine doesn't care what the load is, be it a hill, headwind, taller tire, or seven humans onboard… An increase in load will increase stress on the engine.

Can you find someone nearby to trade wheels with for a day or so?

Robbie
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airkooledchris
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PostPosted: Mon Feb 12, 2018 2:15 pm    Post subject: Re: 27" tires. Will it cause overheating issues?!? Reply with quote

Every setup is so far from stock these days it's hard to say we are ever comparing apples to apples - but in my 79 I found it was better to have the lower revs and higher load when it came to head temps.

My oil was getting really hot on long slow hill climbs, with taller tires, where my head temps went up slightly when I switched to the BFG's (which are slightly shorter than stock I believe.)

I switched back and forth and hit the same hill a few different times and in the end, there didn't seem to be enough of a difference between the 27x8.5R14's and the BFGs to warrant wanting to switch one way or the other. When my current BFG's run their course, ill prob switch back to 27's again.
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MidWesty79
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PostPosted: Mon Feb 12, 2018 3:23 pm    Post subject: Re: 27" tires. Will it cause overheating issues?!? Reply with quote

I have a dakota digital CHT gauge. I run well over 400 degrees cruising on the hwy. Generally 415 or so. I try to keep it under 420, though there are days that even that becomes very difficult. I have posted for years about my high head temps with no real solution presented. I have tried all sorts of things to no avail. I have driven with these head temps for 30K miles or so and *knock on wood* have seen no ill effects.

airkooledchris- Interesting that you saw no negative change with the taller tires and subsequent lower RPMs.

It'd be great to find someone with some taller tires to do some testing. I'll have to look around.
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Gregg in the 603
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PostPosted: Mon Feb 12, 2018 5:27 pm    Post subject: Re: 27" tires. Will it cause overheating issues?!? Reply with quote

Quote:
I run well over 400 degrees cruising on the hwy. Generally 415 or so. I try to keep it under 420


Many here would say you're nuts for running at those temps! Others (SGKent) will say that's normal. I'm going to agree with him, those temps are normal for 65-70 mph. My temps are very similar to yours, and I'm done being nervous about them. Run it!
I do have a potentiometer installed in series with the TSII so I can richen the mixture when I need to, just to get the temps down when absoulutely necessary.
The tremendous improvement in guages over the years has given us so much information. I'm going to say too much. What did they do back in the day, before we had guages to obsess over? Oh that's right, they enjoyed the ride.
Get the Grabbers and let us know how it goes. I love those tires and would love to run them future.
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Shaun Murray
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PostPosted: Mon Feb 12, 2018 6:09 pm    Post subject: Re: 27" tires. Will it cause overheating issues?!? Reply with quote

I ran the 27'' Grabbers on my '79 Westy I sold a few years back. I drove it daily for over a year, and then took it on a cross country trip with them. Drove all over the Rockies loaded heavy with 5 people on board and didn't have any problems related to the tires. I loved them. I currently getting ready to "unlower" my '72 and I'm pretty sure I'll be investing in another set of these once I get it raised back up.
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bigbore
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PostPosted: Mon Feb 12, 2018 8:05 pm    Post subject: Re: 27" tires. Will it cause overheating issues?!? Reply with quote

My 81 Vanagon runs at 350 to 400 no matter hills cold or hot even in Alaska winter it still at 325/350 it's the oil temp I have to watch.
Last summer I was climbing out of Dawson city Yukon at 100F for 8 miles clean out of the tree line and it still stayed at 400F but my oil temp went to the moon about 225/230 when I got to the top at tick over the oil light was flickering now this was the rebuilt engine first run I mean I stuffed the engine in the day before and hit the road for a 1000 mile run.
When I got home I did it first oil change and went to 20W50 mobile 1 and that brought the temp right on down and the pressure never again dropped that low at tick over.
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Bulli Klinik
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PostPosted: Tue Feb 13, 2018 7:59 am    Post subject: Re: 27" tires. Will it cause overheating issues?!? Reply with quote

I ran 15" wheels and BFG's on my Dormobile for years. The idea of driving through the mighty Rockies vs the reality is something altogether different. If you are really in the mountains, you are constantly changing gears regardless of tire size to go up, downshift, make turns, etc... I really like the bigger tire (28's) because it allowed me to run in third up the passes at 50-55.
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airkooledchris
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PostPosted: Tue Feb 13, 2018 2:08 pm    Post subject: Re: 27" tires. Will it cause overheating issues?!? Reply with quote

Gregg in the 603 wrote:
Quote:
I run well over 400 degrees cruising on the hwy. Generally 415 or so. I try to keep it under 420


Many here would say you're nuts for running at those temps! Others (SGKent) will say that's normal. I'm going to agree with him, those temps are normal for 65-70 mph. My temps are very similar to yours, and I'm done being nervous about them. Run it!
I do have a potentiometer installed in series with the TSII so I can richen the mixture when I need to, just to get the temps down when absoulutely necessary.
The tremendous improvement in guages over the years has given us so much information. I'm going to say too much. What did they do back in the day, before we had guages to obsess over? Oh that's right, they enjoyed the ride.
Get the Grabbers and let us know how it goes. I love those tires and would love to run them future.



I have always ran those temps in my current bus, but like Gregg I also run a potentiometer up on the dash and toggle over to that and adjust the mixture as needed - if needed. I actually run pretty lean most of the time now, and just hit the switch and go rich when I need to hit the highway for a while.
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MidWesty79
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PostPosted: Wed Feb 14, 2018 7:39 am    Post subject: Re: 27" tires. Will it cause overheating issues?!? Reply with quote

I have seen mention of the potentiometer trick in the past. Anyone have a link to the install? I'm thinking it would be a very handy add on for me.
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airkooledchris
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PostPosted: Wed Feb 14, 2018 1:52 pm    Post subject: Re: 27" tires. Will it cause overheating issues?!? Reply with quote

The following threads have more information on this setup.

https://www.thesamba.com/vw/forum/viewtopic.php?t=640615&start=20
https://www.thesamba.com/vw/forum/viewtopic.php?t=248511&highlight=potentiometer
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Gregg in the 603
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PostPosted: Wed Feb 14, 2018 5:26 pm    Post subject: Re: 27" tires. Will it cause overheating issues?!? Reply with quote

Quote:
I'm thinking it would be a very handy add on for me


Game changer. A/C Chris shared this idea with me, you'll see in the link.
This hack takes the fear of highway speeds and huge CHT's away.
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MidWesty79
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PostPosted: Thu Feb 15, 2018 7:30 am    Post subject: Re: 27" tires. Will it cause overheating issues?!? Reply with quote

Thanks! I'll definitely have to give this a go!
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